1. Field of the Invention
The invention relates to a multi-way valve having at least three valve connections, of which at least one pair of adjacent valve connections is connected fluidically in a first valve position and is separated fluidically in a second valve position and at least one further pair of adjacent valve connections is separated fluidically in the first valve position and connected fluidically in the second valve position, and an upper part, a lower part and a plate-shaped central part, which is connected to the upper part with the interposition of a first membrane and to the lower part with the interposition of a second membrane.
2. Description of the Related Art
U.S. Pat. No. 6,453,725 B1 disclose a conventional multi-way valve.
U.S. Pat. No. 5,203,368 A discloses an individual valve having a plate-shaped upper part, a lower part and a central part, between which and the lower part a membrane is disposed. The lower part contains a recess which is opposite to two openings in the central part. Depending on whether an overpressure or vacuum is generated in the recess using a control fluid, the membrane closes or releases the openings. The openings are connected via passages with grooves on the side of the central part facing away from the membrane. The grooves covered by the overlying upper part form laterally extending fluid channels, which lead to valve connections.
U.S. Pat. No. 5,496,009 A discloses a multi-way valve in the form of a valve matrix with at least four valves, in order to connect at least two inflow channels individually with at least two outflow channels. The multi-way valve has a plate-shaped upper part, a lower part and a central part, where a membrane is disposed between the upper part and the central part and a sealing film is disposed between the lower part and the central part. The inflow channels are formed by parallel grooves on the upper side of the central part, which are covered by the membrane. The outflow channels are formed by parallel grooves extending horizontally thereto on the lower side of the central part, which are covered by the sealing film. The upper part contains a recess for each valve in each case, where the recess, in the central part, is opposite to one of the inflow channels and an opening connected with one of the outflow channels. Depending on whether an overpressure or vacuum is generated in the recess using a control fluid, the membrane closes or releases the opening and the inflow channel.
The multi-way valve known from the afore-cited U.S. Pat. No. 6,453,725 B1 can be used for sample dosing and separation column switchover in gas chromatography. Here, for instance, in a first valve position, a sample taken from a technical process is routed in a continuous stream through a dosing loop with a defined dosing volume, for instance. At the same time, a separation device of the gas-phase chromatograph consisting of a separation column or a number of connected separation columns is purged with a carrier gas. In a second valve position, the sample quantity contained in the dosing loop is guided through the separation device via the carrier gas, broken down into different sample components and then detected, while the sample flow is routed past the dosing loop.
One example of a conventional multi-way valve is shown cross-sectionally in FIG. 1, in FIG. 2 in a longitudinal section along line AA′, in FIG. 3 in a schematically convoluted section along circular line BB′ in a first valve position, and in FIG. 4 in a second valve position.
The multi-way valve consists of a cylindrical upper part 1, a cylindrical lower part 2 and a central part 3, in the form of a cylindrical plate, which is connected with the upper part 1 with the interposition of a first membrane 4 and with the lower part 2 with the interposition of a second membrane 5. Ten valve connections 6a-6j are mounted on the central part 3 in the circumferential direction and at the same angular distance from one another, by way of which valve connections fluids that are to be switched or distributed to the valve are supplied or are guided out of the valve. For each valve connection 6a-6j, in each case the central part 3 contains a channel system, e.g., 7i, with a first opening 8i on the upper side of the central part 3, a second opening 9i on the lower side of the central part 3 and a third opening 10i for connection with the valve connection 6i. In the example shown, the channel system 7i consists of a channel section connecting the openings 8i and 9i on the upper side and lower side of the central part 3 in the quickest way with one another and a channel section branching therefrom centrally in a T-shape in the direction toward the valve connection 6i. 
With the conventional multi-way valve shown by way of example, there is provision for the adjacent valve connections 6a and 6b, 6c and 6d, 6e and 6f, 6g and 6h and 6i and 6j which each form a pair to be connected fluidically with one another in the first valve position shown in FIG. 3 and to be separated fluidically in the second valve position shown in FIG. 4. Further pairs of adjacent valve connections 6b and 6c, 6d and 6e, 6h and 6i, and 6j and 6a are conversely separated fluidically in the first valve position and connected fluidically in the second valve position.
The fluidic connection or separation of the various pairs of adjacent valve connections is performed with the aid of the two membranes 4 and 5, by these alternately being applied with pressure or relieved of pressure on their side facing away from the central part 3. To this end, on its side facing the first membrane 4, the upper part 1 contains a recess 11 for each pair of adjacent valve connections, e.g., 6a and 6b to be connected fluidically in the first valve position, which recess is opposite to the first openings 8a, 8b assigned to the relevant pair on the upper side of the central part 3.
With the pairs of adjacent valve connections, e.g., 6b and 6c, which are to remain separated in the first valve position, there is no shared recess in the upper part 1 that is opposite to the assigned first openings 8b, 8c, so that at this location the membrane 4 is pressed by the upper part 1 directly against the central part 3 and thus separates the first openings 8b, 8c from one another. All recesses 11 are connected by way of channels 12 to a first control fluid connection 13, by way of which the first membrane 4 can be loaded or unloaded with a control fluid 14 (pressurized air) which can be activated or deactivated.
The lower part 2 similarly contains a recess 15 on its side facing the second membrane 5 for each pair of adjacent valve connections, e.g., 6b and 6c, to be connected fluidically in the second valve position, where the recess is opposite to the second openings 9b, 9c assigned to the relevant pair on the lower side of the central part 3. With the pairs of adjacent valve connections, e.g., 6a, 6b or 6f, 6g that are to remain separated in the first valve position, there is no shared recess in the lower part 2 that is opposite to the assigned second openings 9a, 9b or 9f, 9g so that at this location the second membrane 5 is pressed by the lower part 2 directly against the central part 3 and thus separates the second openings 9a, 9b or 9f, 9g from one another. All recesses 15 are connected by way of channels 16 with a second control fluid connection 17, by way of which the second membrane 5 is loaded or unloaded with the control fluid 14 which can be activated or deactivated.
In the first valve position shown in FIG. 3, the second membrane 5 is loaded with the control fluid 14, while the first membrane 4 is unloaded. The second membrane 5 therefore joins to the central part 3 and closes the second openings 9a-9j. In contrast, the unloaded first membrane 4 eases the pressure of the fluid supplied to the valve via individual valve connections 6a-6j and recedes into the recesses 11, so that the second first openings, e.g., 8a and 8b, are released and the assigned valve connections 6a, 6b are connected fluidically with one another.
In the second valve position shown in FIG. 4, the first membrane 4 is loaded with the control fluid 14, while the second membrane 5 is unloaded. The first membrane 4 therefore joins to the central part 3 and closes the first openings 8a-8j. In contrast, the unloaded second membrane 5 eases the pressure of the fluid supplied to the valve and recedes into the recesses 15 so that the opposing second openings, e.g., 8b and 8c, are released and the assigned valve connections 6b, 6c are connected fluidically to one another.
On account of the dead volumes of the conventional multi-way valve, its use can be restricted in certain applications. For instance, the valve connection 6b in the first valve position is supplied with a first fluid by way of the valve connection 6a and in the second valve position is supplied with a second fluid via the valve connection 6c. During or immediately after switchover from the first into the second valve position, a part of the channel system 7b, i.e., the dead space of the now closed first opening 8b up to the center of the channel section disposed between the openings 8b and 9b, is filled with the first fluid, which then diffuses into the second fluid with a delay. With the example from the gas chromatography mentioned in the introduction, the first fluid can be the sample that is routed through the dosing loop during the first valve position and in the second valve position is transferred via the carrier gas out of the dosing loop into the chromatographic separation device. The diffusion of the sample from the dead volume into the carrier gas results in an imprecise injection of the sample into the flow of carrier gas, which results in a reduction in the resolution of the subsequent chromatographic separation (peak with shoulders).